1. Field of the Invention
The present invention relates to a successive approximation analog to digital (A/D) converter and a conversion method thereof More particularly, the present invention relates to a successive approximation A/D converter with a filtering function and a conversion method thereof.
2. Descriptions of the Related Art
Analog to digital (A/D) converters play a very important role in the digital times. The A/D converters are viewed as bridges between analog signals and digital signals, and are mainly used to convert the analog signals into digital signals so that the converted digital signals conform to signal formats required in digital circuits. Then, the digital signals can be processed by subsequent digital circuit stages. There are many types of A/D converters, examples of which include flash-type A/D converters, pipeline-type A/D converters, and successive approximation A/D converters that have become more popular over recent years, and so on.
In practical applications, an analog signal is often passed through a filter first to filter out unnecessary bands of the analog signal before it is fed into an A/D converter. This can make the band of the filtered analog signal conformable to specifications of the A/D converter so that the filtered analog signal is more suitable for subsequent conversion. Alternatively, after the analog signal is converted into a digital signal, a digital filter is then used to filter the digital signal. However, the additional filter will increase the area of the whole circuit and manufacturing costs. Therefore, it is a great challenge for related manufacturers to make a compromise between the manufacturing cost and conversion performances.
In view of this, an urgent need exists in the art to provide a solution capable of imparting a filtering function to a conventional A/D converter so that desirable signal conversion performances can be achieved at a low cost.